Abstract P4-15-10: Second breast events after DCIS: Where, what and when?

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Abstract Background: Detection and diagnosis of ductal carcinoma in situ has substantially increased since the widespread use of mammographic screening with the incidence of DCIS increasing between 1975 from 5.8 per 100,000 to 33.8 per 100,000 women in 2010. While surgical resection of DCIS remains the main treatment, outcomes in terms of in breast re-occurrence or contralateral disease are unpredictable. Recently, three large clinical trials of active surveillance versus standard of care have been initiated. We sought to compare the clinical, imaging, histopathological features and treatment of DCIS for contemporary patients who subsequently developed a second in situ or invasive breast lesion among women treated within a single institution. Methods: A contemporary prospective cohort study comprising 2,509 women treated for DCIS between 2000 and 2014 was examined for diagnostic imaging, surgery, pathology, adjuvant treatment and second breast events. Patients with primary bilateral DCIS or a bilateral second event were excluded as were patients with antecedent invasive breast cancer. Patients were grouped into two populations based on ipsilateral and contralateral second breast event. Results: Amongst 2,509 women treated for DCIS between 2000 and 2014, of whom 146 had a second breast event (5.8%). 77 (52.7% of events, 3.07% overall) developed an ipsilateral second breast event (37 DCIS, 40 invasive breast cancer) and 69 (47.3%, 2.75%) patients developed a contralateral second breast lesion (34 DCIS, 35 invasive breast cancer). Patients who developed a contralateral second event were older than those who developed an ipsilateral second event (58 years vs. 52 years, p=0.003). Patients receiving segmental mastectomies were more likely to develop an ipsilateral second event than a contralateral event (85.7% vs. 60.9%, p=0.001). Patients who developed a second contralateral breast event were significantly older at diagnosis (63 years vs. 58 years, p=0.003). There was no significant difference in the number of (69 vs. 77) or time between contralateral and ipsilateral second breast events (5.2 years and 5.1 years, p=0.8) nor in the number of patients with invasive or in situ second events (75 vs. 71). Patients with ipsilateral second breasts events were more likely to undergo bilateral mastectomy than those with contralateral second events (15 vs. 2, p=0.003). Conclusions: Following standard of care treatment for DCIS, 1 in 20 women develop further DCIS or invasive disease at a median of 5 years with very similar proportions of ipsilateral or contralateral and DCIS or invasive disease. Current trials of active surveillance should consider a median 5 years follow up as a critical time point for reporting results. Key Words: Ductal carcinoma in situ, invasive breast cancer, population-based cohort, surgery, radiotherapy, endocrine therapy. Citation Format: King LM, Yi M, Krishnamurthy S, Hunt KK, Thompson AM. Second breast events after DCIS: Where, what and when? [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-15-10.